Part of the reliability requirements for radio navigation aids is monitoring of the emitted signals to ensure that the navaid is performing to an operationally acceptable standard. To achieve this, special Field Strength Monitors are used. If the emitted field strength drops below an acceptable value, the navaid can be removed from service until it is fixed.

The photo above shows a DCA Technician, possibly Bill Green, measuring the field strength of the Melbourne/Essendon Visual Aural Range (VAR) radio beacon, which can be seen in the background. This was the first VAR beacon installed in Australia, in 1947, and it is likely that these measurements are being made at around that time. The field strength measurement is being made at the same distance from the beacon that a Field Strength Monitor, below, will be installed.

The photo at left shows the Essendon VAR permanent Field Strength Monitor being given some 'delicate adjustment' after being installed on its post. The Technician is Max Byrne and the supervising Engineer is Alec Dillon.

Click here to see more photos of the Essendon VAR

(Photos: Col Durrell collection)

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